Door closers are mainly applied to fireproof doors in commercial and public buildings. Besides having the function of ordinary doors, fireproof doors also have the function of preventing the spread of fire and smoke, and can prevent the spread of fire within a certain period of time, ensuring that people canevacuate. Fireproof doors usually include a normally closed fireproof door and a normally opened fireproof door, wherein the normally opened fireproof door normally keeps an opened state, so that people can pass through conveniently and ventilation and daylighting are convenient, the normally opened fireproof door can close automatically under a fire situation, playing the role of blocking smoke and fire, consequently, the problems of inconvenience brought to the passage of people by that the fireproof door is closed normally and the artificial damage to the fireproof door caused by frequent opening and closing are solved thoroughly, and moreover, fire safety is also guaranteed.
Under the opened state of a currently common normally opened fireproof door, a door closer will usually fix the door at an extreme opening position or fix the door at any position between the extreme opening position and a closing position. Under the normal use state of such a normally opened fireproof door, both the opening angle and position of a door leaf cannot be adjusted, the opening degree of the door cannot be adjusted at any time according to environmental change or use requirements, so the flexibility is poor.